[mutter/gbsneto/effects-paint-nodes: 2/8] clutter/effect: Add paint_node vfunc

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit a3ec4b1adeeebdbcb4a937c60410617316916ed5
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Sat Jun 27 12:12:03 2020 -0300

    clutter/effect: Add paint_node vfunc
    
    Introduce a new paint_node vfunc that, if implemented, allows
    the effect to add nodes to a transient paint node that is
    immediately painted. This is a transitional step until we
    have fully delegated paint node rendering.
    
    The most basic implementation of a ClutterEffect.paint_node
    vfunc is with an actor node, as follows:
    
    ```
    static void
    foo_bar_paint_node (ClutterEffect           *effect,
                        ClutterPaintNode        *node,
                        ClutterPaintContext     *paint_context,
                        ClutterEffectPaintFlags  flags)
    {
      g_autoptr (ClutterPaintNode) actor_node = NULL;
    
      actor_node = clutter_actor_node_new (effect->actor);
      clutter_paint_node_add_child (node, actor_node);
    }
    ```
    
    This example gives the exact same behavior of simply calling
    clutter_actor_continue_paint(). In the future, the paint node
    itself will be a parameter of clutter_actor_continue_paint()
    and we'll be able to simplify it event more.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1340

 clutter/clutter/clutter-effect.c | 22 +++++++++++++++++++++-
 clutter/clutter/clutter-effect.h |  4 ++++
 2 files changed, 25 insertions(+), 1 deletion(-)
---
diff --git a/clutter/clutter/clutter-effect.c b/clutter/clutter/clutter-effect.c
index 399e7b3cca..25ef613807 100644
--- a/clutter/clutter/clutter-effect.c
+++ b/clutter/clutter/clutter-effect.c
@@ -169,6 +169,7 @@
 #include "clutter-effect-private.h"
 #include "clutter-enum-types.h"
 #include "clutter-marshal.h"
+#include "clutter-paint-node-private.h"
 #include "clutter-private.h"
 #include "clutter-actor-private.h"
 
@@ -213,7 +214,26 @@ clutter_effect_real_paint (ClutterEffect           *effect,
   pre_paint_succeeded = effect_class->pre_paint (effect, paint_context);
 
   actor = clutter_actor_meta_get_actor (actor_meta);
-  clutter_actor_continue_paint (actor, paint_context);
+
+  if (effect_class->paint_node)
+    {
+      ClutterPaintNode *node;
+      CoglFramebuffer *framebuffer;
+      ClutterActor *actor;
+
+      actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (effect));
+      framebuffer = clutter_paint_context_get_framebuffer (paint_context);
+      node = _clutter_dummy_node_new (actor, framebuffer);
+
+      effect_class->paint_node (effect, node, paint_context, flags);
+
+      clutter_paint_node_paint (node, paint_context);
+      clutter_paint_node_unref (node);
+    }
+  else
+    {
+      clutter_actor_continue_paint (actor, paint_context);
+    }
 
   if (pre_paint_succeeded)
     effect_class->post_paint (effect, paint_context);
diff --git a/clutter/clutter/clutter-effect.h b/clutter/clutter/clutter-effect.h
index 8e8b57b92f..d15015cf9e 100644
--- a/clutter/clutter/clutter-effect.h
+++ b/clutter/clutter/clutter-effect.h
@@ -87,6 +87,10 @@ struct _ClutterEffectClass
   void     (* paint)               (ClutterEffect           *effect,
                                     ClutterPaintContext     *paint_context,
                                     ClutterEffectPaintFlags  flags);
+  void     (* paint_node)          (ClutterEffect           *effect,
+                                    ClutterPaintNode        *node,
+                                    ClutterPaintContext     *paint_context,
+                                    ClutterEffectPaintFlags  flags);
   void     (* pick)                (ClutterEffect           *effect,
                                     ClutterPickContext      *pick_context);